Infrared is a type of light that we cannot see with our eyes. Our eyes
can only see what we call visible light. Infrared light brings us special
information that we do not get from visible light. It shows us how much
heat something has and gives us information about an object's temperature.
Everything has some heat and puts out infrared light. Even things that we
think of as being very cold, like an ice cube, put out some heat. Cold objects
just put out less heat than warm objects.
The warmer something is the more heat it puts out and the colder
something is the less heat it puts out. Hot objects glow more brightly in the
infrared because they put out more heat and more infrared light. Cold objects
put out less heat or infrared light and appear less bright in the infrared.
Anything which has a temperature puts out heat or infrared light.
In the infrared images shown below, different colors are used to represent
different temperatures. You can find out which temperature a color represents
by using the color-temperature scale show to the right of most of the images.
The temperatures are in degrees Fahrenheit.

To the left is an infrared image of a metal cup holding a very hot drink.
Notice the rings of color showing heat traveling from the liquid through
the metal cup. You can see this in the metal spoon as well.
To the right is an infrared image of a melting ice cube. Notice the rings
of color showing how the melt water warms as it travels away from the cube.
Although the ice cube is cold, it still puts out heat, as you can see by
matching the color of the ice cube with its temperature.

A visible light picture (left) and an infrared picture (right) of two cups.
One cup contains cold water, while the other contains hot water.
In the visible light picture we cannot tell, just by looking,
which cup is holding cold water and which is holding hot water.
In the infrared image, we can clearly "see" the glow from the hot water in the
cup to the left and the dark, colder water in the cup to the right.
If we had infrared eyes, we could tell if an object was hot or cold without
having to touch it.

By using special infrared cameras, we can get a view of the infrared world.
These cameras are very useful and have even helped save people's lives.
In the infrared, you can "see" in the dark. Even if the Sun is
down and the lights are off, the world around us still puts out some heat.
The infrared picture to the right shows deer in a forest during a dark
night. Notice how we can clearly see the heat from the deer, especially
from areas not covered with thick fur like the ears, face and legs.
The trees and the ground put out less heat than the deer, but can
still be seen through an infrared camera.

Warm-blooded animals, like people, try to keep the same body temperature
during both the day and the night. Their body temperatures do not change
when it gets dark or cold outside and their heat remains about the same.
This makes infrared cameras very useful for finding people who are lost at
night or lost at sea. The warm body heat from a person will cause them to
glow brightly in the infrared, even in the dark or floating in a cold sea.
Police can use infrared cameras to find criminals hiding in the dark and
firefighters also use infrared cameras to find the hot spots in a fire.

Black and white infrared image of a person lost at sea at night
(Courtesy of Raytheon Commercial Infrared).
Notice how this person glowed
in the infrared even when he could not be seen in visible light.

Infrared cameras are also a good way to study warm-blooded animals at night,
and are used to study how animals use fur, feathers and blubber to keep
themselves warm. They are also useful for showing the difference between
warm and cold-blooded animals. To learn more about warm and cold-blooded
animals visit our
The Infrared Zoo
website.

Above are infrared images of a warm-blooded dog (left) and of a warm-blooded human
holding a cold-blooded caterpillar (right).
Warm-blooded animals, like the dog shown above, make their own heat.
In the infrared picture you can see how the dog's fur keeps some of this
heat from escaping, keeping the dog warm.
Insects are cold-blooded, which means that they cannot make their own body
heat. Instead they take on the temperature of their surroundings. The
cold-blooded caterpillar appears very dark (cool) in the infrared compared to
the warm-blooded human who is holding it. Notice how the caterpillar is
at about the same temperature as the surrounding air.

Another interesting fact about infrared light is that it can travel through
thick smoke, dust or fog, and even some materials.

Above is a visible (left) and infrared (right) view of a person's hand inside a black plastic
bag. In the visible image, the hand cannot be seen. In the infrared image,
however, the heat from the hand can travel through the bag and can be seen
by an infrared camera. Infrared light can pass through many
materials which visible light cannot pass through. However, the reverse is
also true. There are some materials which can pass visible light but not
infrared. Notice the man's glasses! Infrared cannot travel through glass.
Since this man's body heat cannot travel through his glasses, they appear
dark.

Because infrared light can travel through thick smoke and visible light cannot,
infrared cameras are used by firefighters to find
people and animals in smoke filled buildings.
The infrared body heat from people and warm-blooded animals can
travel through the smoke and cause them to show up clearly through an infrared
camera.
Many people and their pets have been saved by firefighters using infrared
cameras. Also, because infrared
light can travel through thick fog, it is very useful to have infrared cameras
on ships and airplanes to help in navigation.

courtesy of Sierra Pacific Infrared

courtesy of Mitsubishi Electronics

To the left is a black and white infrared image showing a person trapped in
thick smoke. Firefighters using infrared cameras could find and rescue this
person. The image to the right shows the visible and infrared views from
an airplane as it tries to land in thick fog. In visible light, the runway
cannot be seen. An infrared view, however, allows the pilot to
see the runway and land safely.

Infrared cameras are also used by satellites in space to measure the
temperature of the oceans, to study the Earth's weather during both the day and
night, and to study the infrared light from outer space.

To the left is an infrared map of sea surface temperatures, with red being
the warmest and purple the coldest. To the right are two images taken by
telescopes of a thick area of gas and dust in space where stars are born.
Since infrared can travel through thick dust, astronomers can see through
thick clouds of dust and gas in space by using infrared telescopes. On the
left is a space cloud as seen by a visible light telescope. Notice
that we cannot see what lies behind the cloud. In the infrared view (right)
we can see through the cloud and find bright, young stars which have just
been formed.

There are many other valuable things that we can learn by viewing the world
in the infrared. To learn more about this visit our web site
"Seeing Our
World in a Different Light". It is written for ages 14 and up, so if
you have any trouble understanding the text; ask your parents, guardians, or
teachers to go over this site with you.

Infrared light is only one of the types of light that we cannot see with our
eyes. There are many more, such as X-rays, gamma-rays, ultraviolet light
and radio waves. Each of these different types of light brings us new
information that we cannot get by using our eyes alone.
We are very lucky that we live in a time when we have technology that
allows us to "see" all of these types of light.